This invention relates to the monitoring of a physiological characteristic of a patient, and, more particularly, to establishing a warning limit that may be used to indicate a variation of the physiological characteristic that necessitates immediate attention.
Advances in sensor technology, electronics, and communications have made it possible for physiological characteristics of patients to be monitored even when the patients are ambulatory and not in continuous, direct contact with a hospital monitoring system. For example, U.S. Pat. No. 5,959,529 describes a monitoring system in which the patient carries a remote monitoring unit with associated physiological sensors. The remote monitoring unit conducts a continuous monitoring of one or more physiological characteristics of the patient according to the medical problem of the patient, such as the heartbeat and its waveform.
Under prescribed conditions, the remote monitoring unit contacts a central unit to communicate information on the condition of the patient. The communication may be accomplished in some cases on a routine reporting basis (e.g., a regular once-a-day report at night on a land telephone line while the patient sleeps) and in other cases on an urgent basis that signifies an event wherein the patient may need immediate attention (e.g., over a cellular telephone link as the patient experiences discomfort or an attack). The remote monitoring unit contains logic, which may be generally be described as a warning limit, that is used to determine whether the communication is to be made on an urgent basis. The warning limit is usually based both on the nature of an evaluation criterion for specific events and also on a quantitative threshold for the selected criterion.
In the studies leading to the present invention, the inventor has observed that the application of these fundamental principles of warning limits is straightforward conceptually but complex in practice. Although many physiological characteristics may be described in a textbook manner, large variations from the textbook description are encountered in everyday situations. For example, variations in sensor performance, individual human characteristics and responses, personal experiences, and the like make it difficult to establish warning limits that are universally applicable, or even applicable for the same patient under all conditions.
The warning limits are normally selected in a conservative manner when viewed from the standpoint of patient safety. That is, it is preferable to make urgent communications more often than necessary, rather than to fail to make an urgent communication when it is necessary. On the other hand, too many urgent communications are wasteful in terms of power consumption of the remote monitoring unit (establishing and maintaining a cell phone connection consumes a relatively large amount of power and thus reduces available battery life), telephone connection time expense, and resource use at the central unit.
For these reasons, it is important to establish realistic warning limits characteristic of situations that are truly urgent. There are not currently available any approaches which meet this requirement, and consequently a need exists for establishing warning limits for use in such situations. The present invention fulfills this need, and further provides related advantages.
The present approach provides a technique for monitoring a patient in which one or more warning limits are recursively reevaluated as necessary. Proposed changes to the warning limits are made without human intervention, but in some cases the proposed changes may be reviewed by a human being to be certain that they are realistic. The present approach is fully compatible with adjustments to warning limits made by medical personnel. The present approach allows a patient monitoring system to be continuously refined and customized for the individual patient and the individual monitoring system through an adaptive learning process.
In accordance with the invention, a method of monitoring a patient comprises the steps of establishing a current warning limit for a physiological characteristic of the patient. A sensor is provided for the physiological characteristic. such as the heartbeat, for example, and a measured value of the physiological characteristic of the patient is measured using the sensor. The measured value and the current warning limit are compared, and a warning signal may be generated responsive to the step of comparing in the event that the measured value is outside the value defined by the current warning limit. The method includes selecting a revised warning limit responsive to at least one of the steps of providing and measuring, preferably without human intervention (i.e., automatically). However, a human being may review the revised warning limit. That is, the automated system may propose the revision, subject to revision by the human being.
The step of selecting a revised warning limit may be made responsive to any of a wide variety of circumstances. For example, the operating characteristics of the sensor may be determined, and the selecting of the revised warning limit may be made responsive to the determination of the operating characteristics of the sensor. The selecting of a revised warning limit may instead be responsive to the step of measuring, as where the step of measuring is performed as a function of time, and wherein the step of selecting is responsive to time variations in the measured value or is responsive to a value of time. The selecting of the revised warning limit may be additionally responsive to a second physiological characteristic or to a patient history.
In one embodiment, the present invention is practiced using a monitoring apparatus including a remote monitoring unit associated with the patient, a central unit, and a communications device which selectively establishes a communications link between the remote monitoring unit and the central unit responsive to a warning signal. This apparatus provides a real-time urgent communications capability. It may also be practiced in other operable situations, such as monitors whose data are periodically transmitted, non-ambulatory situations, and the like.
The present invention allows the patient to be monitored and acceptable limits for the physiological conditions of the patient to be defined increasingly precisely over time. With continued experience as the monitoring apparatus adapts to the individual patient, the incidence of unnecessary urgent communications is expected to decrease. The result is that the efficiency of resource utilization is expected to increase over time. Additionally, the monitoring apparatus discovers which warning limits are most meaningful for the individual patient, so that the precision of the generation of warnings is increased.